Port 882055ff

Original commit message:
- fix truthfulness of comments
- use InitializeFieldsWithFiller more consistently
- use unsigned comparisons for pointers

No change in functionality intended.

Bonus: improve JavaScriptFrame::Print() for an enhanced debugging experience:

- print PC of each frame
- print the function's source also for optimized frames

R=dstence@us.ibm.com, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1193363004

Cr-Commit-Position: refs/heads/master@{#29197}